1. Field of the Invention
The present invention relates to a dust collecting apparatus for purifying various exhaust gases containing dust, and more particularly to a dust collecting apparatus constructed to collect dust from the exhaust gases introduced therein for discharging the gases in a clean condition.
2. Description of the Prior Art
Disclosed in Japanese Patent Laid-open Publications Nos. 271808/1992 and 354506 is a dust collecting apparatus of this kind which includes a plurality of ceramic filter elements aligned in parallel within a housing, each of the filter elements being made of porous ceramic material and having a thin walled cellular structure formed with a plurality of axially extending passages separated from each other by thin partition walls, wherein a first group of the axial passages are closed at their one ends in a checked pattern and opened at their other ends to introduce therein exhaust gases to be purified, while a second group of the axial passages are opened at their one ends to discharge purified gases therefrom and closed at their other ends in a checked pattern, the housing being provided with an outlet duct located at a downstream side of the filter assembly. In the dust collecting apparatus, exhaust gases to be purified are introduced into the first group of the axial inlet passages at an upstream side of the filter assembly so that the thin partition walls of the filter elements act to collect dust from the exhaust gases permeating therethrough from the first group of the axial inlet passages into the second group of the axial outlet passages thereby to purify the exhaust gases. The purified gases are discharged from the housing through the outlet duct while fine particles of the dust are accumulated on the surfaces of the partition walls. During such treatment of the exhaust gases, washing gas under pressure is intermittently supplied into the filter assembly through the outlet duct and flows into the second group of the axial outlet passages to flow into the first group of the axial inlet passages through the partition walls. Thus, the accumulated fine particles are separated from the partition walls.
In such a conventional dust collecting apparatus as described above, the outlet duct is in the form of a spout duct formed with a plurality of equally spaced jet nozzles. The spout duct is spaced in a predetermined distance from the downstream end of the filter assembly to introduce washing gas under high pressure into the second group of the axial outlet passages therefrom for washing the filter elements. In such an arrangement of the spout duct, the reverse washing efficiency of the filter elements is greatly affected by the pressure of washing gas applied to the second group of the axial outlet passages. It is, therefore, required to increase the spout pressure of the washing gas as high as possible for enhancing the reverse washing efficiency of the filter elements. In the dust collecting apparatus, however, the washing gas is directly applied to the downstream side of the filter elements from the jet nozzles of the spout duct. As a result, a portion of the washing gas is discharged outwardly from a discharge duct provided on the housing for discharge of the purified gases. This causes a decrease of the pressure of the washing gas introduced into the second group of the outlet passages and fluctuation of the spout pressure of the jet nozzles, resulting in irregular separation of the accumulated dust at the partition walls.